POWDERY MILDEW INFECTION ON SOME EGYPTIAN BREAD WHEAT CULTIVARS IN RELATION TO ENVIRONMENTAL CONDITIONS.

Wheat  powdery mildew, caused by the biotrophic fungus Blumeria graminis (DC) E.O. Speer  f. sp. tritici Em. Marchal, is one of the most severe foliar diseases attacking this crop, affecting wheat production under Mediterranean basin conditions through the last few years. Four bread wheat cultivars i.e.. Sakha-93, Gemmeiza-7, Gemmeiza-10, and Giza-160 as a check were evaluated to artificial inoculation of powdery mildew under field conditions. The tested wheat cultivars showed susceptible responses to powdery mildew with fluctuated values in 2010 and 2011 seasons. In 2010 season, the tested cultivars showed high levels of disease severity, ranged from 35 to 87 % ( Gemmeiza-7 and Gemmeiza-10, respectively). While, in 2011 lower levels were recorded, from 6.00 up-to 15% ( Sakha-93 and Gemmeiza-10, respectively). Area under disease progress curve (AUDPC) was correlated with disease severity during the two seasons. Also, the yield components, the thousand grain weight and the grain yield/m2 were affected by disease severities with different values for each cultivar. High air temperature, wind speed and mild relative humidity played an important role in increasing powdery mildew infection level  in 2010 season.